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Synlett 2015; 26(12): 1702-1704
DOI: 10.1055/s-0034-1380740
DOI: 10.1055/s-0034-1380740
letter
Investigations on the [2,3]-Wittig Rearrangement of Chiral 4-Aminopropargyloxy Acetates to Novel α-Hydroxy-γ-amino Acids Containing an Allene Unit
Further Information
Publication History
Received: 02 April 2015
Accepted after revision: 14 April 2015
Publication Date:
11 May 2015 (online)
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Abstract
The [2,3]-Wittig rearrangement of propargyloxy acetates bearing a propargylic stereocenter opposite to the oxyacetic acid moiety gives α-hydroxy-γ-amino acids containing an allene unit under high stereocontrol. The resulting product displays a novel type of γ-amino acid with a potentially intriguing biological profile.
Supporting Information
- Supporting information for this article is available online at http://dx.doi.org/10.1055/s-0034-1380740.
- Supporting Information
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References and Notes
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- 10 Synthesis of tert-Butyl (2R,4S)-4-[(tert-Butoxycarbonyl)amino]-2-hydroxy-6-methyl-3-(2-methylprop-1-en-1-ylidene)heptanoate (13): Under an atmosphere of argon, i-Pr2NH (230 mg, 2.27 mmol) was dissolved in anhydrous THF (2 mL) and charged with n-BuLi (1.6 M in n-hexane, 2.16 mmol, 1.33 mL) at –78 °C. The solution was stirred at –78 °C for 1 h followed by the dropwise addition of 12 (210 mg, 0.55 mmol) dissolved in anhydrous THF (3 mL). The mixture was stirred at 78 °C for 1 h and at –70 °C for 3 d. The mixture was quenched with sat. aq NaHCO3 (5 mL). H2O (2 mL) was added and the mixture was extracted with Et2O (3 ×). The combined organic phases were washed with brine and sat. aq NaHCO3. Subsequently, the organic phase was dried and concentrated. The crude product was analyzed by 1H and 13C NMR spectroscopy. The spectra showed only signals of 12 and 13. The corresponding stereoisomer of 13 was not observed. Finally, the residue was purified on silica gel (Et2O–pentane, 1:4 v/v). Yield: 21 mg (0.05 mmol, 14% based on recovered starting material). 1H NMR (200 MHz, CDCl3): δ = 0.91 [d, J = 6.8 Hz, 3 H, CH2-CH(CH 3)2], 0.93 [d, J = 6.8 Hz, 3 H, CH2-CH(CH 3)2], 1.30–1.49 [m, 2 H, CH 2-CH(CH3)2], 1.44 [br s, 9 H, C(CH 3)3], 1.48 [s, 9 H, C(CH 3)3], 1.59–1.67 [m, 1 H, CH2CH(CH3)2], 1.71 and 1.72 [2 s, 6 H, C=C=C(CH 3)2], 3.54 (d, J = 7.6 Hz, 1 H, CHOH), 4.27–4.33 (m, 1 H, NHCH), 4.42 (d, J = 9.6 Hz, 1 H, NHCH), 4.46 (d, J = 7.6 Hz, 1 H, CHOH). 13C NMR (50 MHz, CDCl3): δ = 20.04, 20.36, 22.36, 22.83, 24.99, 28.09, 28.41, 43.97, 48.17, 71.12, 79.36, 81.99, 101.20, 104.57, 155.40, 172.58, 199.06. MS (EI): m/z (%) = 29 (17.25), 41 (27.93), 57 (100.00), 86 (59.50), 124 (11.85), 130 (42.03), 136 (12.08), 226 (10.12), 253 (22.69); MS (CI, NH3): m/z = 384 [M + H]+. Anal. Calcd for C21H37NO5 (384.53): C, 65.77; H, 9.72; N, 3.65. Found: C, 65.80; H, 9.66; N, 3.66